Decontamination solution and method



United States Patent 3,258,429 DECONTAMINATION SOLUTION AND METHODRonald D. Weed, Richland, Wash., assignor to the United States ofAmerica as represented by the United States Atomic Energy Commission NoDrawing. Filed Sept. 19, 1963, Ser. No. 310,176 7 Claims. (Cl. 252301.1)

The invention described herein was made in the course of, or under, acontract with the United States Atomic Energy Commission.

The invention relates to :a novel decontamination solution, and to amethod of decontaminating liquid-containing systems of nuclear reactorsemploying the same. More particularly, the invention relates to asolution suitable for, and to a method of, decontaminating aqueousmoderator and coolant circulation systems in reactors having steel orzirconium structural materials.

In the operation of a nuclear reactor, failure of fuel element cladding,both small and on a large scale, is an ever present possibility.Following a fuel element failure, quantities, sometimes quite large, offissionable material are carried by the circulating coolant or moderatorand deposited throughout the liquid-containing system. Removal of theseis necessary not only because of the radioactive and toxic nature of thefissionable material itself but even more because of the highlyradioactive fission products which are embedded within it.

The task of decontaminating the coolant or moderator system iscomplicated by the chemical complexity of the materials requiringremoval. When the fuel is an actinide metal, and where the temperatureof the water is high as in the case of pressurized water-cooledreactors, the contaminating material is usually in the form of a mixtureof actinide oxides such as U0 U 0 U0 PuO and the like, and oftenincluded are particulate pieces of actinide metal, sometimes ofconsiderable size.

An'especially diflicult decontamination situation arises when plutoniumdioxide is involved. This oxide and the other oxides of plutonium arenotoriously hard to dissolve, and resist nitric acid almost completely.Finally, decontaminating solutions must not corrode the structural metalof the coolant circulation system to an unacceptable extent.

In the past, nitric acid has been used as a decontaminant; in additionto its inability to dissolve Pu0 this decontaminant is unacceptablycorrosive to carbon steel and to brass alloys. Mixtures of phosphoricacid and hydrogen peroxide have been used, but have been found to beseverely corrosive. Solutions containing permanganate ion have beentried, but these tend to leave deposits of manganese dioxide which aredifficult to remove completely. Many other solutions have been proposedbut all have had some drawback; either they dissolved the oxides inquestion but not the metal, or they dissolved the metal but not theoxide, or else their corrosion characteristics made them impractical.

It is, accordingly, the general object of the invention to provide anelfective, practical method of decontaminating nuclear reactorliquid-containing systems.

It is :a more particular object to provide such a method for a nuclearreactor liquid-containing system which is contaminated with a mixture ofactinide oxides, actinide metal and fission products.

It is a concurrent object of the invention to provide a decontaminatingsolution capable of dissolving a mixture of actinide oxides, actinidemetal and fission products.

Other objects will appear as the description proceeds.

The foregoing objects are attained by decontaminating a reactorliquid-containing system with a five component ice aqueous solution, thefirst four components of which are oxalic acid, sodium oxalate, hydrogenperoxide and 8-quinolinol. An example of these first four components isas follows:

( 1) Oxalic acid, about 2.3 grams per liter (2) Sodium oxalate, about 32grams per liter (3) Hydrogen peroxide, about 15 grams per liter (4)8-quinolinol, about 1 gram per liter It is :to be understood that theterm per liter refers to a liter of the entire solution including thefifth component now to be described.

The fifth component is a member of the class consisting of 40% by weightaqueous peracetic acid, and a 2 to 1 by weight mixture of sodiumgluconate and 50% by weight aqueous gluconic acid.

When the fifth component is the aqueous peracetic acid, it may bepresent in the solution at the rate of about 12.5 grams per liter ofsolution.

When the fifth component of the solution is the mixture above referredto the components of the mixture may be present in the solution asfollows:

Sodium gluconate, 5 to 40 grams per liter, Gluconic acid (aq. 50%), 2.5to 20 grams per liter,

the term liter again being understood to be a liter of the entiresolution, and the 2 to 1 by weight ratio above mentioned always beingobserved.

This solution, regardless of which of the two fifth components ischosen, is effective in decontaminating reactor liquid-containingsystems, and is well within the limits of acceptable corrosive action inthe case of systems containing carbon steel, stainless steel, Inconel,zirconium and brass. The solution has certain advantages depending onwhich of the two fifth components is chosen, as will be seen in theexamples later on.

To use the decontaminating solution, the coolant or moderator water,which, of course, may be either light or heavy water, is emptied fromthe contaminated system. The decontaminating solution is then put intothe system in an amount approximately equal to the normal amount ofcoolant or moderator and the circulation means such as a pump is turnedon. The withdrawn coolant or moderator is analyzed to determine itsdegree of contamination; this is done most readily :and accurately bycounting its radioactivity in a disintegration counter. From time totime portions of the decontaminating solution are withdrawn, freshportions put in, and the withdrawn portions are counted forradioactivity. When the count of a withdrawn portion reaches a safelevel the decontaminating solution is withdrawn completely and thesystem is flushed with light water a sufiicient number of times toremove all traces of the solution. If the coolant or moderator is heavywater, the system is flushed additionally with heavy water a sufficientnumber of times to remove all traces of the light water.

EXAMPLE I A decontaminating solution was made up as follows, it beingunderstood that the term liter refers in all cases to a liter of theentire solution and that the peracetic acid is aqueously dilute, itspercentage indicated being by weight based on the weight of the diluteacid:

Six portions of the solution were taken out and placed in glass flasks.A mixture of uranium oxides were placed Table I 4 to make it a superiordecontamination means for nuclear reactor liquid-containing systems, andthat at the same time its rate of corrosion is acceptable for steel,stainless steel, zirconium alloys and brasses.

EXAMPLE II A decontaminating solution was made up as follows, it againbeing understood that the term liter refers in all cases to a liter ofthe entire solution and that the DATA FOR DISSOLUTION OF URANIUM OXIDESWITH THE OXALIO-PEROXIDE- PE RACETIO SOLUTION Amount 01 Oxides Added toSolution g./l. 50 g./l. 75 g./l. TSIEIL,

Initial Final Gins. U per Initial Final Gms. U per Initial Final Gins. Uper pH pH Liter in pH pH Liter in pH pH Liter in Solution SolutionSolution 4. 12 4. 32 16.9 4. so 4. 50 19.8 (l) (l) 80 4. 4. 53 16. 6 t)60 4. 30 4. 51 15. 1 4. 30 4. 52 23. 9 4. 38 4. 57 24. 2

1 Tests not conducted.

20 more portions of the same decontaminating solution were taken, andinto each was placed a weighed metal coupon, of one of the followingmetals: ordinary or carbon steel (CS); 304 stainless steel (304 SS); 302stainless steel (302 SS); Inconel-X; Zircaloy; common, or as it is alsoknown, red brass; and admiralty brass, or as it is also known, admiraltymetal. These portions were maintained at three different temperatures,80 C., 60 C. and 40 C., and after a period of time the coupons wereremoved, rinsed, dried, weighed, and their corrosion rates in mils perhour calculated from the loss of weight of the coupons in the usualmanner. The results of these tests are set forth in Table II.

Table II gluconic acid is aqueously dilute, its percentage indicatedbeing by weight based on the weight of the dilute acid:

This solution was subjected to the same tests as those described inExample I, with a few minor variations,

CORROSION (MILS/IIOUR) OF MATERIALS IN TIIE OXALIC-PEROXIDE- PERACETICSOLUTION 1 N .D.=none detected.

The above two series of tests indicate that the decon- 55 which areindicated in Tables III and IV, below, which taminating solution withperacetic acid as the fifth component dissolves uranium oxides to anextent sufficient DATA FORQDISSOLUTION OF URANIUM set out the results ofthe tests in the same manner as Tables I and II.

Table III OXIDES WITII THE OXALIC-PEROXIDE- GLUCONIC SOLUTION Amount ofOxides Added to Solution Temp. 25 g./l. 5O g./l. g./l.

Initial Final Gms. U per Initial Final Gms. U per Initial Fin Gms. U perpH pH L1ter in pH pH Liter in pH pH Liter in Solution Solution Solution1 Tests not conducted.

Table IV GLUCONIC SOLUTION Materials Tem p CS 304 SS 302 SS InconeLXZircaloy-2 Brass Adligniralty 80" 0.005 N.D. 0.001 0. 001 1N.D. 1.721.00 00 0. 002 N.D. 0.001 N.D. N.D. 0.77 0.02 40 0. 001 N.D. N.D. N.D.N.D. 0.12

1 N .D.=none detected.

These tests indicate that my decontaminating solution grams of uraniumdissolved per liter at the end of the with the fifth component in thisexample is likewise an hour for the solution on the same horizontalline. efficient means of dissolving uranium oxides, with desir- Table Vably low corrosion characteristics. It has the additional advantage ofnot being susceptible to explosion. 5 X ggg fgffi g i$gi g EXAMPLE IIIG1 A'd sd G1 t G ULt' The decontaminating solution of Example I was used(lonc dl l i zigioif ./1.) Co nc t a ii t rati i i ggelle) elut ioh m ina simulated test of decontaminating a contaminated light Watercore-coolant circulation system of a nuclear 2.5 5.0 29.0 reactor havingfuel elements of PuO Irradiated Pu0 8:8 $38 52:; from a reactor core andlight water were placed in a 20.0 40.0 27.3 shielded cask and attachedto a loop of pipe having a circulating pump, a system in inlet andoutlet valves, and a 1 GlllCOlilc acid (50%). filter The above dataindicates that the concentrations of T eorjslstmg the cask and loop wassodium gluconate and gluconic acid may be varied withmalntamed 300 andafter one hour the Water was in the limits tested without changing thedissolution cadrained from the system through the filter and the filterpabilifies of the Solution was teeunted radloaeuvlty' It was feund to beIt will be understood that the invention is not to be men gens Per ilimited to the details given herein but that it may be Thedecontaminating solution described in Example I modified within theScope of appended claims. was then circulated through the system for onehour at The embodiments of the invention in which an 0 80 The solutionwas dramtd ehe System and elusive property or privilege is claimed aredefined as the system was then flushed twice with Water and the follows,radioactivity in the filter was counted. It was found to L An aqueousdecontaminating solution consisting of be e'ztmentgens Per hour or areduetlon of about 63 40 oxalic acid, sodium oxalate, hydrogen peroxide,S-quinos efi t th fin d h d t linol, and a member of the classconsisting of aqueous eye em en e W1 t e econ ammatlng peracetic acidand a 2 to l by weight mixture of sodium solution of Example II and thesame steps were carried gluconate and 50 percent by Weight aqueousgluconic out under the Same eondltlens' The acid, the components of saidsolution being present in tmg fa loaetmty on the filier was found to beamounts sufiicient to decontaminate an aqueous coolant roentgens perhour, or a reduction of about 33 percent. System ofanuclear reactor Thlsexample Shows i my Solutlen 'q 2. An aqueous decontaminating solutionconsisting esrneans for decontaminating nuclear reactorliquid-containsemiany f about 23 grams per liter of oxalic acid about mgY Q Tegardless Wh 1ch of two fifth 32 grams per liter of sodium oxalate,about 15 grams per T between the Percentages liter of hydrogen peroxide,about 1 gram per liter of 8- of reduetlon of radloacnvltyi 63% and ofquinolinol, and a member of the class consisting of 40 9 an accurate fle of the cm Parat 1ve percent by weight of aqueous peracetic acidpresent in ciencies of the two variations of the solution since the theproportions of 125 grams per liter and a 2 to 1 by concentration ofradioactive material was much larger weight mixture of sodium gluconatei 50 percent by at the Start the test e f f the Mass Action Law a weightof aqueous gluconic acid, the said sodium glularger reduction ofradioactivity at the start was only to conate being present in theproportions of from about 5 be expected. EXAMPLE W to about 40 grams perliter and the said aqueous gluconic acid being present in theproportions of from about 2.5 to about 20 grams per liter In order toevaluate the capabilities of my decontami- 3. An e t ifiiefitlilonsolution when the concentration was varied of the sentiauy s 1 3,? 223;??? g g ggi i ig t component of the sodium gluconate-gluconic acidabout 32 -r ms 1 ripe, a furtlliler series of dissolution tests wasmade. In grams per i f igdifg g gfy i dg gigi iii i 2:1 t ese tests t etemperature was held constant at 40 C i iter of 8- uinolinol and abi512: iniialhnu-mber of grams of U per liter of solution at 40percentqby weight of gfi p g g z g liter of an t e time at one hour. Thesodium gluconate 4 A 11 aqueous decontaminating solution COl'lSlStll'l"was varied from 5 to 40 grams per liter of solution and e essentially ofabout 2.3 grams er liter of oxal' d the 50% gluconic acid was variedfrom 2 5 to 20 g /l P 1C 301 about 32 grams per liter of hydro eneroxide ab t 1 the 2 to 1 ratio by weight between these in all casesbeing a g p on gram er liter of 8- uinolinol bo observed. In all otherrespects these tests were carried 7 f sodgum gluconateqand abolltas g igi g g out under the same conditions as described in previous Percent byWeight of aqueous gluconic acid Ex irrlifilesvI eiiid II. h 1 5. Amethod of decontaminating a fluid-containing sysa e 0W5 t e g Uconlcacid and Sodlum f tem of a nuclear reactor, comprising contacting thesys- COHCeIltratlOnS the f Component of y solution 111 tern with anaqueous decontaminating solution consisteach test, and in the right handcolumn the number of ing essentially of about 2.3 grams per liter ofoxalic acid,

about 32 grams per liter of sodium oxalate, about 15 grams per liter ofhydrogen peroxide, about 1 gram per liter of 8-quinolinol, and a memberof the class consisting of 40 percent by weight of aqueous peraceticacid present in the proportions of 12.5 grams per liter, and a 2 to 1 byweight mixture of sodium gluconate and 50 percent by weight of aqueousgluconic acid, the said sodium gluconate being present in theproportions of from about 5 to about 40 grams per liter and the saidaqueous gluconic acid being present in the proportions of from about 2.5to about 20 grams per liter.

6. A method of decontaminating a fluid-containing system of a nuclearreactor, comprising contacting the system with an aqueousdecontaminating solution consisting essentially of about 2.3 grams perliter of oxalic acid, about 32 grams per liter of sodium oxalate, about15 grams per liter of hydrogen peroxide, about 1 gram per liter ofS-quinolinol, and about 12.5 grams per liter of 40 percent by weight ofaqueous peracetic acid.

7. A method of decontaminating a fluid-containing system of a nuclearreactor, comprising contacting the systcm with an aqueousdecontaminating solution consisting essentially of about 2.3 grams perliter of oxalic acid, about 32 grams per liter of hydrogen peroxide,about 1 gram per liter of '8-quinolinol, about 10 grams per liter ofsodium gluconate, and about 5 grams per liter of 50 percent by weight ofaqueous gluconic acid.

References Cited by the Examiner AEC Document I-IW-67937,Decontamination Studies for Hapo Water-Cooled Reactor Systems, Dec. 27,1960, pages 22-38.

LEON D. ROSDOL, Primary Examiner.

S. TRAUB, Assistant Examiner.

1. AN AQUEOUS DECONTAMINATING SOLUTION CONSISTING OF OXALIC ACID, SODIUMOXALATE, HYDROGEN PEROXIDE, 8-QUINOLINOL, AND A MEMBER OF THE CLASSCONSISTING OF AQUEOUS PERACETIC ACID AND A 2 TO 1 BY WEIGHT MIXTURE OFSODIUM GLUCONATE AND 50 PERCENT BY WEIGHT AQUEOUS GLUCONIC ACID, ANDCOMPONENTS OF SAID SOLUTION BEING PRESENT IN AMOUNTS SUFFICIENT TODECONTAIMINATE AN AQUEOUS COOLANT SYSTEM OF A NUCLEAR REACTOR.
 5. AMETHOD OF DECONTAMINATING A FLUID-CONTAINING SYSTEM OF A NUCLEARREACTOR, COMPRISING CONTACTING THE SYSTEM WITH AN AQUEOUSDECONTAIMINATING SOLUTION CONSISTING ESSENTIALLY OF ABOUT 2.3 GRAMS PERLITER OF OXALIC ACID, ABOUT 32 GRAMS PER LITER AND SODIUM OXALATE, ABOUT15 GRAMS PER LITER OF HYDROGEN PEROXIDE, ABOUT 1 GRAM PER LITER OF8-QUINOLINOL, AND A MEMBER OF THE CLASS CONSISTING OF 40 PERCENT BYWEIGHT OF AQUEOUS PERACETIC ACID PRESENT IN THE PROPORTIONS OF 12.5GRAMS PER LITER, AND A 2 TO 1 BY WEIGHT MIXTURE OF SODIUM GLUCONATE AND50 PERCENT BY WEIGHT OF AQUEOUS GLUCONIC ACID, THE SAID SODIUM GLUCONATEBEING PRESENT IN THE PROPORTIONS OF FROM ABOUT 5 TO ABOUT 40 GRAMS PERLITER AND THE SAID AQUEOUS GLUCONIC ACID BEING PRESENT IN THEPROPORTIONS OF FROM ABOUT 2.5 TO ABOUT 20 GRAMS PER LITER.